In a typical head, an inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium. Since magnetic flux decays as it travels down the length of the narrow second pole tip, shortening the second pole tip will increase the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS.
FIG. 1A illustrates, schematically, a conventional recording medium such as used with conventional magnetic disc recording systems. This medium is utilized for recording magnetic impulses in or parallel to the plane of the medium itself. The recording medium, a recording disc in this instance, comprises basically a supporting substrate 100 of a suitable non-magnetic material such as glass, with an overlying coating 102 of a suitable and conventional magnetic layer.
FIG. 1B shows the operative relationship between a conventional recording/playback head 104, which may preferably be a thin film head, and a conventional recording medium, such as that of FIG. 1A.
As longitudinal recording is expected to reach its maximum at about ˜140 Gbit/in2 due to the superparamagnetic effect, efforts have been focused on perpendicular recording to extend areal density.
FIG. 2A illustrates schematically the orientation of magnetic impulses substantially perpendicular to the surface of the recording medium. For such perpendicular recording the medium includes an under layer 302 of a material having a high magnetic permeability. This under layer 302 is then provided with an overlying coating 304 of magnetic material preferably having a high coercivity relative to the under layer 302.
Two embodiments of storage systems with perpendicular heads 300 are illustrated in FIGS. 2A and 2B (not drawn to scale). The recording medium illustrated in FIG. 2B includes both the high permeability under layer 302 and the overlying coating 304 of magnetic material described with respect to FIG. 2A above. However, both of these layers 302 and 304 are shown applied to a suitable substrate 306.
By this structure the magnetic lines of flux extending between the poles of the recording head loop into and out of the outer surface of the recording medium coating with the high permeability under layer of the recording medium causing the lines of flux to pass through the coating in a direction generally perpendicular to the surface of the medium to record information in the magnetically hard coating of the medium in the form of magnetic impulses having their axes of magnetization substantially perpendicular to the surface of the medium. The flux is channeled by the soft underlying coating 302 back to the return layer (P1) of the head 300.
FIG. 2C illustrates a similar structure in which the substrate 306 carries the layers 302 and 304 on each of its two opposed sides, with suitable recording heads 300 positioned adjacent the outer surface of the magnetic coating 304 on each side of the medium.
One area of research in perpendicular head design is focused on developing a manufacturable fabrication process to form the write pole. Unlike longitudinal head design whereby the write pole aspect ratio is ˜4:1, perpendicular write pole design requires a 2:1 aspect ratio and ˜15 degree bevel to minimize adjacent track interference. As areal density approaches 120 Gb/in2 or higher, the write pole's trackwidth scales down to 140 nm or lower. At these dimensions, write pole instability (reminiscent issues, e.g., writing continuing after power to head is terminated) becomes an issue and requires implementing lamination technology in the write pole. Lamination, however, forecloses use of plating to form the write pole.
In the fabrication aspect, factors such as HSU, shield thickness from the air bearing surface (ABS), and gap controls are important in achieving the angling effect of the effective write field. During fabrication, the gap must be tightly controlled. In slider lapping, the shield thickness from the ABS must be precisely controlled. The parameters presented below must be considered to achieve optimal effective write field.
The constant demand for higher areal density has aggressively pushed for narrower trackwidth. Since the perpendicular write pole's aspect ratio is 2:1 and as the write pole trackwidth approaches ˜102 nm for 200 Gbit/in2 areal density, the thickness of the write pole will be about the thickness of a typical seed-layer. The difficulty in fabricating a trailing shield write pole is designing a process to have tight control of the write gap and fabricating a structure on top of the write gap with minimal damage to the write gap or write pole. Precise control of the gap thickness is important because if the gap is too thin, too much flux goes to the shield. If the gap is too thick, the flux angle into the media is not desirable, as the flux is most effective when entering the media at an angle (e.g., 45°) with respect to disk surface. Thus, the gap thickness must be near perfect.
The improvements of the single pole trailing shield (SPT) design of the invention over the single pole (SP) design can be explained by the Stoner-Wohlfarth model. FIG. 3 is a plot of H-grain angle as a function of the main grain angle. It can be seen that for a distribution of grain angles, increasing the angle between H and the mean grain angle can decrease the distribution of switching fields by ½ thus increasing the effective field by 2× and decreasing jitter.
FIG. 4 is a partial side view of a writer 400. The optimal field angle is achieved in the design when the distance (HSU) from the ABS to the soft underlayer of the media 402 is equal to the length of the write gap (GAP), which is the distance between the end of the trailing shield 404 and the write pole 406. The write field is decreased as the shield 404 is brought closer to the write pole piece 406 because part of the flux is increasingly shared between the soft underlayer of the media 402 and the trailing shield 404. This problem is ameliorated by controlling the thickness of the trailing shield 404, GAP, HSU, and bringing the flare point of the write pole closer to the ABS.
To get the optimized effective field angle, the gap and shield thickness need to be tightly control as shown in FIG. 5.
The benefits provided by such a design include:                1) Increased dH/dX        2) Reduced partial erasure        3) Improved saturation        4) Reduced media noise        5) Tilt field eases writing on S-W media.        
In the past, damascene and image transfer technologies (DITT) were considered as methods to form the 15 degree beveled 2:1 aspect ratio of the write pole. However, due to the need to implement lamination to reduce write instability these technologies were found to be undesirable.
Ion milling is emerging as an alternative approach to DITT to fabricate laminated write poles, but is not directly extendable to a trailing shield write pole design whereby the gap thickness between the write pole and shield (trailing shield) is tightly controlled.
Moreover at submicron trackwidth dimension, the pole piece as fabricated by ion milling will be fragile and removal of redeposited materials on top (redeposition) and sides (fencing) of the pole will be increasingly more difficult.
What is needed is an effective and reliable way to fabricate a laminated write pole and write gap of a precise thickness for use in a perpendicular recording head.
The present invention introduces a method and materials to fabricate a trailing shield write pole that resolve the problems of controlling the write gap and preventing damage to the write gap or pole during fabrication of the subsequent structure. This process also introduces a CMP assisted lift-off process to remove redeposition and fencing (to increase yields) and a method to create curvature in the write pole.